1. Technical Field
The present invention relates to a roll paper supply mechanism that stores roll paper so that it can roll on its side in a roll paper storage unit, and delivers and conveys a continuous web of recording paper from the roll paper storage unit to a printing position of a printer, for example. More particularly, the invention relates to a roll paper supply mechanism and to a roll paper printer having a roll paper supply mechanism that is configured so that the roll paper does not lift up from the bottom of the roll paper storage unit or a feed-out roller disposed at the bottom of the roll paper storage unit.
2. Related Art
Roll paper printers such as those used to print receipts and tickets use roll paper, which is a continuous length of recording paper wound into a roll, as the recording medium, and typically have a so-called drop-in loading type of roll paper storage unit as a roll paper supply mechanism. The roll paper is simply dropped from above and loaded into the roll paper storage unit so that the roll paper can roll on its side, and the roll paper supply mechanism delivers and conveys the continuous web of recording medium from the roll paper to the printing position. The recording paper delivered from the roll paper stored in the drop-in type roll paper storage unit is set threaded through a transportation path passed the paper feed rollers and printing position to the paper exit, and as the recording medium is conveyed by the paper feed rollers, the roll paper rolls on its side inside the roll paper storage unit (also referred to as a roll paper compartment) as the recording medium is delivered downstream.
If the roll paper shifts sideways as the recording medium is pulled from the roll, problems such as the recording paper becoming skewed and the paper feed load varying can occur. More particularly, when the widthwise position of the roll paper is limited only by left and right roll paper guides that determine the roll paper storage width in the roll paper compartment, and the widthwise position of the recording medium is not guided on the transportation path passed the printing position, the roll paper must be stored so that it does not shift sideways inside the roll paper compartment.
The round end faces of the roll paper are therefore commonly urged by an elastic member so that there is no side ways play or shifting widthwise to the paper. In addition, so that the roll paper is not held at an elevated position by the elastic force of the elastic member when the roll diameter decreases and the roll paper becomes light, the roll paper is urged with a strong elastic force when the roll diameter is large, and the roll paper is urged by a weaker elastic force when the roll diameter becomes small. Japanese Unexamined Patent Appl. Pub. JP-A-2005-306535 teaches a roll paper holding mechanism having this type of elastic member.
With a drop-in type roll paper compartment it is also necessary to cause the roll paper to roll and to deliver the recording paper in resistance to the inertial load of the roll paper and the friction between the roll paper and the bottom of the roll paper compartment. If the paper feed speed is increased, the paper feed load that works on the paper feed rollers also increases accordingly, possibly resulting in paper feed slippage and a drop in paper feed precision. Therefore, in order to reduce the paper feed load and feed the paper with precision, Japanese Unexamined Patent Appl. Pub. JP-A-2007-203563 and Japanese Unexamined Patent Appl. Pub. JP-A-2007-203564 teach roll paper supply mechanisms that have a delivery roller for causing the roll paper to rotate in the delivery (that is, the paper feed) direction disposed at the bottom of the roll paper compartment.
Even with the roll paper supply mechanism having a delivery roller as taught in JP-A-2007-203563 and JP-A-2007-203564, however, the roll paper must be urged widthwise by an elastic member in order to prevent the roll from shifting sideways because the width of the roll paper compartment is set slightly greater than the width of the roll paper in order to accommodate deviations in the roll paper width. If in this configuration the urging force of the elastic member that is used to prevent sideways movement holds the roll paper above the bottom of the roll paper compartment when the roll diameter decreases and the roll paper becomes light, the roll paper will separate from the delivery roller and causing the roll paper to roll and delivering the recording paper may not be possible.
Providing an elastic member that pushes against the roll paper with a strong elastic force when the roll diameter is large and pushes against the roll paper with a weak elastic force when the roll diameter becomes small as taught in JP-A-2005-306535 is therefore preferable to prevent the roll paper from being held above the delivery roller when the roll diameter becomes small.
However, even when the urging force of the elastic member decreases in accordance with the decrease in the roll diameter of the roll paper as taught in JP-A-2005-306535, the roll paper cannot be reliably prevented from being held in the raised position. For example, if the force whereby the recording paper is pulled from the roll paper by the paper feed roller, for example, works on the roll paper as a moment in a direction lifting the roll paper up, the likelihood is high that the roll paper will lift up easily. As a result, if the position where the elastic member urges the roll paper is not set appropriately, and only the strength of the urging force is simply controlled according to the roll diameter, the roll paper cannot be reliably prevented from rising up off the bottom or delivery roller.
With a roll paper supply mechanism having a delivery roller, the delivery force of the delivery roller works on the roll paper stored in the roll paper compartment, and the pulling force of the paper feed roller disposed downstream in the printer works at the position where the recording paper is pulled from the roll paper. The roll paper therefore easily rises off of the delivery roller when the roll diameter decreases and the roll paper become slight, and if the urging force of the elastic member decreases, the roll paper can be lifted even more easily off of the delivery roller.
Furthermore, even when the roll diameter is large and the roll paper is heavy, if the recording paper pulling force and the delivery force work on the roll paper as a moment in the direction lifting the roll paper up, the likelihood of the roll paper lifting up is high. The roll paper therefore cannot be reliably prevented from rising away from the delivery roller even if a roll paper supply mechanism having a delivery roller is used if the strength of the urging force alone is simply controlled according to the roll diameter and the urging position of the elastic member against the roll paper is not also set appropriately.